Most prior techniques to treat varicose veins have attempted to heat the vessel by targeting the hemoglobin in the blood and then having the heat transfer to the vessel wall. Lasers emitting wavelengths of 500 to 1100 nm have been used for this purpose from both inside the vessel and through the skin. Attempts have been made to optimize the laser energy absorption by utilizing local absorption peaks of hemoglobin at 810, 940, 980 and 1064 nm. RF technology has been used to try to heat the vessel wall directly but this technique requires expensive and complicated catheters to deliver electrical energy in direct contact with the vessel wall. Other lasers at 810 nm and 1.06 um have been used in attempts to penetrate the skin and heat the vessel but they also have the disadvantage of substantial hemoglobin absorption which limits the efficiency of heat transfer to the vessel wall, or in the cases where the vessel is drained of blood prior to treatment of excessive transmission through the wall and damage to surrounding tissue. All of these prior techniques result in poor efficiency in heating the collagen in the wall and destroying the endothelial cells.
For example, Navarro et al., U.S. Pat. No. 6,398,777, issued Jun. 4, 2002, teaches that it is necessary to have at least some blood in the vein to absorb Diode laser radiation to perform endovenous ablation. More recently, Navarro teaches to remove a significant amount of blood but to leave a layer in the vein to act as an absorbing chromophore for the laser. These lasers in fact will not perform laser ablation of the vein walls with a completely blood free vein.
Goldman et al., in U.S. Pat. No. 6,752,803, issued Jun. 22, 2004, teach the removal of blood with the use of tumescent anesthesia to compress the vein prior to laser treatment. This method has the disadvantage of not completely removing blood from the vessel. It is generally accepted within the art that the most compression that tumescent anesthesia can accomplish is to bring the vessel to about 5 mm in diameter. At this size, a significant amount of blood can remain in the vessel. In fact, since tumescent anesthesia will only compress the vein to a controlled size, the use of tumescent anesthesia has proven to be an excellent way to leave a precisely controlled amount of blood in the vein to act as an absorbing chromophore for hemoglobin targeting lasers such as the 810, 940 and 980 nm diode systems.
On the other hand, recent attention has been paid to endovenous laser ablation techniques using lasers operating at wavelengths that do not require the presence of blood in the vein. For example, Hennings et al., in U.S. Patent Publication No. 2005/0131400, published on Jun. 16, 2005, teaches that lasers operating at wavelengths of from about 1200 nm to about 1800 nm produce laser energy that is more strongly absorbed by the vessel walls than by the blood, in comparison to the lasers operating at lower wavelengths. Accordingly, the lasers and laser ablation techniques described by Hennings will actually operate better when the vein is drained as far as possible.
Regardless of the endovenous laser treatment method used, any blood remaining in the vessel also has the potential of creating additional problems. For example, depending upon the laser system components and their operating parameters, the blood that remains in the vein may coagulate when heated by the laser and cause thrombosis, non closures, or pain and bruising. In addition, small pockets of blood act as heat sinks during the laser treatment and need to be heated to coagulation temperatures in order to adequately ablate the vein wall. One milliliter of blood can absorb close to one joule of energy to raise its temperature one degree Celsius. Since the damage temperature of the vein wall is around 80 degrees C., it could take as much as 50 Joules of energy to raise this small pocket of blood from 30 deg C. The laser treatment dosage is typically only 70 to 80 Jules per centimeter of vein length, so a one milliliter pocket of blood could absorb all of the energy intended to ablate the vein wall in that area leading to a section of non closure of the vein.
Furthermore, if the vein wall is perforated during ablation with blood present, blood may leak out of the vein causing bruising and discoloration of the skin post op.
Still further, during vein ablation, while the vein is shrinking to complete closure, blood left in the vein is squeezed out of the vein through the access point requiring sponging and absorbing pads to clean it up.
Blood will coagulate at about 80° C. Small pockets of blood that have coagulated and remain in the vein can prevent the vein from completely collapsing on itself. This residual thrombus prevents the opposing coagulated vein walls from touching during the healing process and prevents them from healing together. This is a major cause of non closures and failed procedures. Desmyttere et al. described the increased efficacy of endovenous ablation when using a 980 nm diode laser, and when the Trendelenburg position is used to drain the blood prior to treatment. See Jacques Desmyttere et al., “A 2 years follow-up study of endovenous 980 nm laser treatment of the great saphenous vein: Role of the blood content in the GSV,” Elsevier, 19 Aug. 2005. They report closure rates of 91% after 2 years when blood is drained compared to closure of only 74% when the patient is in the horizontal position.
Finally, blood that is coagulated can be forced out of the vein into the remaining venous system and travel through the body as a deep vein thrombosis (DVT). This is a serious and potentially life threatening condition.
For these reasons, and for the reason that the mid infrared laser does not require a blood chromophore to convert laser energy into thermal energy, it would be desirable to have a method for more completely removing blood from the vein prior to endovenous ablation.